North Vietnam supported the Pathet Lao to fight against the Kingdom of Laos between 1958–1959. Control over Laos allowed for the eventual construction of the Ho Chi Minh Trail that would serve as the main supply route for enhanced NLF (the National Liberation Front, the Vietcong) and NVA (North Vietnamese Army) activities in the Republic of Vietnam

The North Vietnamese Communist Party approved a "people's war" on the South at a session in January 1959, and, in May, Group 559 was established to maintain and upgrade the Ho Chi Minh trail, at this time a six-month mountain trek through Laos. On 28 July, North Vietnamese and Pathet Lao forces invaded Laos, fighting the Royal Lao Army all along the border. Group 559 was headquartered in Na Kai, Houaphan province in northeast Laos close to the border. About 500 of the "regroupees" of 1954 were sent south on the trail during its first year of operation. The first arms delivery via the trail was completed in August 1959. In April 1960, North Vietnam imposed universal military conscription for adult males. About 40,000 communist soldiers infiltrated the south from 1961 to 1963.